| ZHAO Liang,XU Yajun,YUAN Ye. 2016. The estimation of a critical shear stress based on a bottom tripod observation in the southwest off Jeju Island, the East China Sea. Acta Oceanologica Sinica, 35(11):105－112 |
| The estimation of a critical shear stress based on a bottom tripod observation in the southwest off Jeju Island, the East China Sea |
| 利用坐底观测估算济州岛西南海域再悬浮临界应力 |
| Received:October 29, 2015 Revised:January 11, 2016 |
| DOI：10.1007/s13131-016-0953-3 |
| Key words:suspended sediment critical shear stress settling velocity East China Sea |
| 中文关键词: 悬浮沉积物 临界应力 沉降速度 东海 |
| 基金项目: |
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| Abstract: |
| The resuspension and deposition of sediment within a bottom boundary layer (BBL) is the main dynamic processes that control the fate of the suspended sediment in shelf seas. The numerical study of sediment transport patterns relies on the knowledge of some critical parameters that describe sediment erosion and deposition. A critical shear stress is estimated based on field observations at the edge of a mud area southwest off Jeju Island, the East China Sea. On the basis of the simultaneous observation of velocity and suspended sediment concentrations within the BBL by means of acoustic instruments including an acoustic Doppler velocimeter and an acoustic Doppler current profiler, the settling velocity is estimated by turbulent oscillations of the SSC under the assumption of inertial-dissipation balance. This method gives a mean value of 0.91 mm/s and standard deviation of 0.20 mm/s, which is an order of magnitude larger than the value obtained by an empirical method of Soulsby and by an in situ submersible particle size analyzer. The difference is possibly due to the distinct natures of two methodologies, the inertial-dissipation method is more indicative of the BBL dynamics and is thus believed to provide reasonable in situ estimates of the settling velocity, whereas Soulsby's method is usually suitable for still water. A novel method for estimating the critical stresses of erosion and deposition based on statistical analyses of the temporal variability of the SSC (which is defined as a derivative of the depth-averaged SSC with respect to time) and the corresponding bottom shear stress is proposed. Both critical stresses of erosion and deposition vary between 0.11 Pa and 0.25 Pa with corresponding median values of 0.20 Pa and 0.16 Pa, respectively, which confirms that the critical stresses of erosion is somewhat higher than the critical stresses of deposition. Another method of estimating the critical shear stress by means of the settling velocity is also employed, which yields reasonable critical shear stress values of 0.06-0.17 Pa. |
| 中文摘要: |
| 底边界层中沉积物的再悬浮和沉降是控制陆架海悬浮沉积物的输运的关键过程。沉积物输运过程的数值*模拟也依赖于沉积物侵蚀和沉降的关键参数的研究。本文根据济州岛西南泥质区的坐底观测估算了此处临界应力。通过底边界层声学仪器ADV和PC-ADP的流速和悬浮物浓度同步观测，基于湍生成与耗散平衡假设，使用惯性耗散法计算沉降速度。这种方法得到的沉降速度ws平均值为0.91 mm s-1，标准差为0.20 mm s-1，此结果远大于Soulbsy（1997）和LISST-ST现场观测粒径分析仪等经验方法的结果。这主要是由于两种方法的本质不同，惯性耗散法形象的刻画了底边界层的水动力，并且更加合理的现场估计沉降速度ws，然而Soulsby的方法通常适用于静水环境。我们提出了一种估计临界应力的新方法，根据悬浮颗粒物浓度时空变化的统计分析（深度平均的悬浮颗粒物浓度对时间求导数）和对应的底应力估算侵蚀临界应力τce和沉降临界应力τcd。侵蚀临界应力τce和沉降临界应力τce的变化范围为0.11-0.25 Pa，对应的中值分别为0.20 Pa和0.16 Pa，这也证实了侵蚀临界应力略大于沉降临界应力。除此之外，我们还使用了另一种方法估算临界应力，通过沉降速度间接估算的临界应力范围为0.06-0.17 Pa。 |
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